1. Field of the Invention
The present invention relates to a method and apparatus for selectively engaging a transducer located on the end face of a rotating transducer drum of an Arcuate Scan Head Assembly (ASHA) with a magnetic tape, and more particularly, a tape support system for achieving consistent head-to-tape coupling throughout the intended recording location, especially at the edges of the tape.
2. Description of the Related Art
Many commercial magnetic tape drive systems utilize a reel-to-reel transport system for passing magnetic tape past a substantially stationary read/write head. Information is typically placed on the tape in the form of a plurality of parallel tracks extending along the longitudinal axis of the tape. The stationary read/write head may have either a single channel or multiple channels. The read/write head may move laterally to read different tracks on the tape, but during the read/write operation the head is essentially stationary. Recording and playback is achieved by moving the tape longitudinally past a read/write zone. Since the read/write head is stationary, achieving good head-to-tape contact is relatively well known. For example, the tape may wrap around the head.
Another widely used tape drive uses a Vertical Helical Scan (VHS) head in which one or more heads are located on the outside of a rotating cylinder or drum. The tape moves over the side surface of the cylinder, wrapping partially around the surface of the cylinder. The cylinder is inclined with respect to the tape path so that each head traces a helical path along the tape. Again, contact between the head(s) and the tape can easily be maintained by wrapping the tape partially around the side surface of the cylinder.
The newly developed arcuate scanning tape drives (see PCT published application WO 93/26005, which is hereby incorporated by reference) utilize a rotating transducer drum with a generally planar end face containing transducers that engage with the tape plane as the tape moves past. In contrast to VHS drives, the axis of rotation of the transducer drum passes through the tape plane. Each transducer therefore reads/writes a sequence of arcuate tracks generally laterally across the tape, hence the name Arcuate Scanning Head Assembly, or ASHA.
With an ASHA, wrapping the tape around the end face of the drum means that the transducers are continuously engaged with the tape through the entire transducing path. This configuration results in accelerated wear on the tape and the read/write heads. Additionally, even though the read/write heads are switched off during a portion of the path opposite the intended recording zone traced by the transducers, the engagement of the heads with the tape results in signal cross-talk that creates noise in the system.
The front face of the transducer drum engaging with the tape surface rotates between approximately 7,500 to 15,000 rpm. Even higher speeds may be used in the future. If the end face of the drum is inserted into the tape plane, this rotation of the transducer drum against the tape plane creates opposing forces generally perpendicular to the longitudinal axis of the tape. In particular, one edge of the rotating drum creates a force transverse to the longitudinal axis of the tape while the opposite edge of the drum creates a force in the opposite direction, resulting in a tendency to twist the tape in the direction of drum rotation. Consequently, it is extremely difficult to achieve intimate head-to-tape contact, particularly at the edges of the tape.
Additionally, the transducers typically extend slightly above the end surface of the transducer drum, e.g., 0.0005 inches (0.0127 mm). If the end face of the transducer drum has the read/write heads located at a diameter larger than the width of the tape, which is generally the case, the transducers may impact on the edges of the tape, potentially causing premature tape failure and damage to the read/write heads.